Final answer:
Alarm calls made by black-tailed prairie dogs potentially affect both their direct fitness and indirect fitness, with the latter referring to protecting relatives and ensuring gene propagation. The same principle applies to the vocalizations of small birds that serve various purposes and influence natural selection. Altruistic behaviors, like a squirrel's warning call, can evolve due to the indirect fitness benefits despite potential costs to direct fitness.
Step-by-step explanation:
When prairie dogs use alarm calls to warn each other of approaching predators, they potentially affect both their direct fitness and indirect fitness. Direct fitness pertains to an individual's own reproductive success, while indirect fitness refers to the reproductive success of an individual's relatives, thereby ensuring that shared genes are passed on. In the case of black-tailed prairie dogs, their alarm calling behavior could potentially reduce their personal chances of survival (and hence their direct fitness), since drawing attention to themselves might make them a target for predators. However, it also serves to protect their kin, thus enhancing their indirect fitness.
Analogously, in the examples provided, scolding and warning calls made by small birds affect natural selection. For instance, a scolding call must be audible to the predator to be effective and hence would be naturally selected for. However, a mobbing call, although potentially alerting the predator, aids in nest defense and provides a collective benefit, also contributing to natural selection.
Finally, the evolution of altruistic behaviors, such as a squirrel warning its peers about a nearby predator, may seem counterintuitive if they decrease the direct fitness of the caller by making it more conspicuous to predators. Yet, if the caller aids the survival of relatives sharing common alleles, the behavior might evolve through natural selection due to benefits to indirect fitness.